1. Preheat oven to 350'F.
2. Spray a 9x13-inch baking dish with non-stick cooking spray; set aside.
3. In a large mixing bowl, melt butter. Set aside to cool at room temperature.
4. Then whisk in sugar, vanilla extract and eggs until well combined.
5. In a separate mixing bowl, sift together flour, cocoa powder, salt and baking powder. Add dry ingredients to wet ingredients and combine well.
6. Microwave Nutella for 20-30 second, or until melted and add to batter.
7. Spread batter into prepared baking pan and bake for 30-35 minutes or until done.